Herbicides



Patented Sept. 15, 1953 HERBICIDES David T. Mowry and Ross M. Hcdrick, Dayton,

pany, St. Louis,

Ohio, assignors to Monsanto Chemical Com- Mo., a corporation of Delaware No Drawing. Application January 3, 1951, Serial No. 204,259

4 Claims.

This invention relates to compositions of matter unusually adapted for destruction of vegetation. More particularly the compositions have unusual properties for preventing various undesirable secondary effects, which frequently occur when ordinary herbicidal compositions are used to destroy growing surface plants.

The use of herbicides of both contact and hormone types to treat undesired vegetation is wellknown and widely practiced. Roadsides, embankments, and other earth surfaces are often subjected to toxic chemicals to prevent brush growth which may become a fire hazard if permitted to accumulate. Similarly, railroad rights of ways may be improved in appearance by controlling plant growth by the action of herbicides. Fire lanes cut in timber land often do more harm than good if surface brush, which grows more abundantly in cleared areas, is permitted. In these several applications herbicides have proved to be of exceptional value.

Herbicides of the conventional type frequently induce undesirable secondary effects due to the tendency to encourage wind and water erosion. Areasv cleared of the normal covering vegetation are more susceptible to the washing by surface water than are areas where vegetation is permitted to grow. The roots of growing plants and the leaf mulch serve to retain the soil particles in their original position. The excessive drying of the soil is avoided and the soil is retained in a moist compacted form, stable to movement by the wind, but the destruction of plants removes the stabilizing attributes. These disadvantages are especially noticeable on lands with sloped surfaces, for example artificial embankments and the surfaces of cuts through hillsides and ridges. Most of the remaining timber is found in hilly country where the use of herbicides to remove fire hazards causes serious washing and loss of top soils and the natural land contours. Similarly road embankments and shoulders in wooded, hilly country, where it is impracticable to seed grass and maintain fire lanes by regular mowing, present serious fire hazards where herbicides are not used, yet the destruction of vegetation will result in intolerable erosion.

The purpose of this invention is to provide a herbicidal composition which will not cause excessive erosion. A further purpose of this invention is to provide methods of destroying surface vegetation without inducing injury to the physical structure of the underlying soil. A still further purpose of this invention is to improve the physical characteristics of soil so that herbi- 2 cides may be used without disadvantageous erosion effects.

In accordance with this invention it has been found that if conventional herbicides are dispersed in certain polymeric carriers, or water solutions thereof, vegetation may be destroyed without permitting the breakdown of the natural crumb structure of the soil. If the vegetation to be destroyed is growing on sub-soil or other soils of poor structure, the desirable porous crumb structure may actually be developed by the use of the new herbicidal compositions. The said water-soluble polymeric carriers are deposited on the plant surface or on the soil surface. The type of toxicant used in combination with the polymeric carriers will influence the manner of application. If the new herbicides are applied to the leaves, they will ultimately reach the ground through the washing action of rainfall.

However they are applied, the polymeric carriers will ultimately become adsorbed to the soil partices and cause the agglomeration thereof into discrete crumbs, which produce the improved physical properties of the soil. The agglomeration of the very fine particles into larger soil particles minimizes the movement of the soil by the action of flowing surface water or windstorms. The same improved soil structure enables the soil to absorb larger proportions of moisture and to retain the moisture for a longer period of time through the minimization of surface evaporation. Soils of improved structure are more readily penetrated by rainfall or other moisture on the sur-- face of the soil whereby the flow of water on the surface in confined channels is eliminated or substantially minimized. The combined effect of allthese properties is to avoid the removal of soil from its normal position by action of wind or Water.

In the culturing of certain crops the use of selective herbicides to effect weed control is widely used in preference to mechanical cultivation by disks, harrows and the like. By this technique considerable economies in Weed control may be effected without direct chemical damage to the crop. However, with soils of poor structure, the impact of rainfall causes slaking of the soil, erosion, severe cracking and the formation of a, hard surface crust. In these cases mechanical cultivation during the growing season also serves to break up this surface crust, which provides a dry surface mulch, reduces evaporation of water and increases aeration in the underlying soil. Although shallow feeder roots are frequently destroyed "by mechanical cultivation, yields of corn tially better yields are achieved when weed control is effected by a mixture of a selective herbicide and the structure improving additive than are achieved either by the use of cultivation or the herbicide alone.

The polymeric carrier for the herbicidal composition is a water-soluble copolymer of a maleic. acid derivative and another polymerizable substance. Suitable copolymers are those represented by the structural formula:

l l t rr (3:0 (3:0 z z" X Y n wherein X and Y may be the same or different radicals of the group consisting of OK, ONa, ONH4, ONRHs, ONRzI-Iz, -ONR3H, ONRA, -OH, --NH2OCH2N-Rz -OCH2-CH2-NR, OR, NC2H4-NR2, NHR and NRz, not more than one of X and Y being OR, and wherein Z, Z, Z" and Z' are radicals of the group consisting of OCOCHa, -,OCOI-I, OH, Cl, -CH3, -COOI-l, CcHs, H, OR, and COOR, a plurality of Z, Z, Z" and Z being hydrogen, and not more than one of the Z, Z, Z and Z being of the group OCOCHs, OH, CaHs, OCOH, OR, COOR and --COOH, and all of the radicals of the group Cl and CH3, being attached to the same carbon atom, R, in the above formula represent ing an aliphatic hydrocarbon radical containing from one to four carbon atoms, and wherein X and Y together may be --O-, and may also be OCa-O.

Suitable maleic acid derivatives useful in the practice are maleic acid, maleic anhydride, maleamic acid, maleic amide, the alkali and alkaline earth metal and ammonium maleic acid salts, the di(p-aminoethyl) maleate, di(methylaminoethyl) maleate, di(N,N-dimethyl p-aminoethyl) maleate, and the various salts, amides and aminoalkyl esters of the alkyl half-esters of maleic acid. Of especial value are the derivatives in which the alkyl radicals have up to four carbon atoms. Similar derivatives of chloroinaleic and citraconic acids may also be used.

Suitable comonomers included within the scope of the invention as set forth in the preceding paragraph are styrene, vinyl chloride, vinyl acetate, ethylene, vinyl for-mate, vinyl alkyl ethers, alkyl acrylates, alkyl metha-crylates, isobutylene, vinylidene chloride, and especially the derivatives wherein the alkyl radical has up to four carbon atoms. One or more of these comonomers may be used.

In general the maleic acid derivatives contribute the water solubility or hydrophilic character of the copolymer and the comonomer is merely an active olefinic compound required to effect a polymerization of the said maleic acid derivative. Usually the comonomer is hydrophobic in character, but acrylic acid and methacrylic acid may contribute to the water solubility of the copolymers. If desired esters, such as alkyl acrylates, alkyl methacrylates, vinyl carboxylates and allyl carboxylates may be hydrolyzed after polymerization to form acrylic and methacrylic acid polymers or vinyl and allyl alcohol polymers. In such polymers the acid or alcohol groups contribute to the desirable hydrophilic properties of the maleic copolymers. The copolymer may have the maleic derivative in the form of the maleic acid anhydride, which may react in part, or entirely, with the water, if an aqueous medium is used to form maleic acid.

Although cross-linked polymers are useful, linear polymers generally produce a better efieot.

Suitable herbicides for use in combination with the polymers for the preparation of the new herbicidal compositions are 2,4-dichlorophenoxyacetic acid and the metal salts, amino salts and esters thereof, the corresponding derivatives of 2,4,5trichlorophenoxyacetic acid, trichloroacetic acid, the various aromatic derivatives of carbamic acid, for example isopropyl-lLphenyl car-. bamate, pentachlorphenol and the soluble salts such as sodium pentachlorphenate, arsenic derivatives, such as sodium arsenate, sodium chlorate, ammonium sulfamate, dinitrophenol and other aromatic nitro derivatives and other compounds known to be toxic to living plant tissues.

The relative proportions of each of the components will depend upen the type of vegetation and the extent of growth to be destroyed, and also upon the specific herbicides used and their relative toxicity. Furthermore, the quantity of carrier used will also be influenced by the need of the soil for structural improvement, the need for an adhesive to prolong contact with the above-ground parts of the plants and to increase the period of effectiveness of the specific herbicide in contact with the ground. In general from 0.05 per cent to 20 per cent by weight of herbicide and from '80 per cent to 99.95 per cent of the polymer will be effective. Preferred practice utilizes from 0.1 per cent to 10.0 per cent by weight of herbicide and 90 per cent to 99.95 per cent of the polymers.

The polymer and herbicide do not merely produce their individual efiects simultaneously, but

there is a complementary or synergistic effect.

The polymers under some circumstances adsorb or occlude the herbicide and thereby retain it in effective form for a longer period by preventing its dissipation by rainfall or destructive action of soil bacteria.

Other benefits will obviously be derived by the proper selection of the specific herbicides and specific polymers which form base chemical compounds capable of dissociation in the soil over a substantial period of time.

What we claim is:

l. A solid composition comprising from 0.05 to 20 per cent by weight of a herbicide and from to 99.95 per cent of a carrier consisting of a water-soluble copolymer having numerous recurring units of the following structure:

Z! Z!!! -CH--CH-( 3-( 0:0 (1:0 i i i t wherein X and. Y are radicals selected from the group consisting of OK, OiNa, --ONH4, ONRH3, ONRzHz, ONRaI-I, ONR4, --OI-I, NHz, OR, OCHzNRz, OCI-IzCHzNRz, NCI-IzCI-IzNRz, NHR and -NR2, not more than one of the X and Y radicals being OR; and

wherein Z, Z, Z", and Z' are radicals selected from the group consisting of -CsH5, OCOH, OCOCH3, -OR, COOR, -COOH, -CH3, OH, Cl and hydrogen, at least two of said groups being hydrogen, not more than one of said groups being of the group consisting of -OCOCH3, -OCOH, -OH, C6H5, --OR, COOH and -COOR, all of the radicals of the group consisting of Cl and CH3 being attached to the same carbon atom, B being an alkyl radical having up to four carbon atoms; and wherein n is an integer indicative of the extent of polymerization; and wherein X and Y together may be O--, and may also be -OCa-O, said ,polymer having a structure derived substantially entirely by polymerization of mono-olefinic compounds.

2. The herbicidal composition as defined by claim 1 wherein from 0.1 per cent to ten per cent by weight of the composition is herbicide.

3. A solid composition comprising a herbicide and a water-soluble polyelectrolyte having a molecular structure derived essentially by the polymerization 01' a mono-olefinic compound through aliphatic unsaturated groups, said polyelectrolyte being a copolymer of at least one compound containing the molecular grouping -c -oH==oH and at least one other mono-olefinic monomer, and being capable of imparting water-stability to soil aggregates.

4. The composition defined by claim 3 wherein from 0.05 to 20% by weight of the composition is a herbicide.

DAVID T. MOWRY. ROSS M. HEDRICK.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,976,679 Flkentscher et al. Oct. 9, 1934 2,380,416 Davidson July 31, 1945 2,536,482 Wood Jan. 2, 1951 

1. A SOLID COMPOSITION COMPRISING FROM 0.05 TO 20 PER CENT BY WEIGHT OF A HERBICIDE AND FROM 80 TO 99.95 PER CENT OF A CARRIER CONSISTING OF A WATER-SOLUBLE COPOLYMER HAVING NUMEROUS RECURRING UNITS OF THE FOLLOWING STRUCTURE: 